Figure 2: Asymmetric dipped beam
The most important measuring points are:
• 50V = 50 metres in front of the vehicle
• 50R = 50 metres on the outer edge of the carriageway (for right-hand traffic)
• 75R = 75 metres on the outer edge of the carriageway (for right-hand traffic)
The FOM value (Figure of Merit) is now the commonly accepted term to measure the quality of the dipped beam. It is calculated from the sum of the light intensity at all measuring points, with the point at 75 metres carrying double weight:
• FOM [Lux] = Light intensity (2 x 75R + 50R + 50V)
The higher the FOM, the better the light. Of course, this assumes that the maximum permissible lighting values (glare values) are not exceeded above the cut-off line.
How an X-tremeVision works
Bulbs like the Philips X-tremeVision, which shines more light onto the road, have a filament that is smaller but brighter. As the luminous surface is smaller, the total amount of light does not change much. However, the headlight can use the available light more effectively to direct it to the distance range described above. The result is a higher FOM: Up to 130% more brightness and a range that is up to 45 metres longer. Of course, this is always somewhat dependent on the headlight system used.
The brighter and hotter filament is also the reason why these particularly powerful bulbs always have a shorter service life than standard bulbs. Philips uses a special, particularly pressure-resistant quartz glass for all its bulbs. A particularly high gas fill pressure of up to 15 bar in the bulb is at least partial compensation for the drawback of its short service life. The 15 bar relates to the pressure when the bulb is cold. When in operation, the pressure within the glass bulb is up to three times greater.
And finally, a note about bulb installation
We are frequently told not to touch halogen bulbs with bare hands, but the biggest problem here is not the oils that can burn into the glass and cause damage, as this would require an enormous level of contamination. What is much worse is even the smallest amount of contaminants that evaporate in the headlights and deposit themselves on the sensitive mirror surfaces. This can cause an unsightly coating to build up relatively quickly, which will affect the lighting quality at some point. So the best thing is to always wear suitable gloves.